The present invention generally relates to fuel-fired heating appliances and, in a preferred embodiment thereof, more particularly provides a gas-fired, forced draft water heater having incorporated therein a specially designed flammable vapor control system operative to substantially prevent entry into combustion within the water heater combustion chamber of extraneous flammable vapors externally adjacent a bottom portion of the water heater without detecting extraneous flammable vapors or terminating firing of the water heater.
Gas-fired residential and commercial water heaters are generally formed to include a vertical cylindrical water storage tank with a gas burner disposed within a combustion chamber below the tank. The burner is supplied with fuel gas through a valved gas supply line, and combustion air through an air inlet flow path providing communication between the exterior of the water heater and the interior of the combustion chamber.
Water heaters of this general type are extremely safe and quite reliable in operation. However, when gasoline or other flammable liquids are stored or used improperly in proximity to the water heater, there may exist a possibility of extraneous flammable vapors externally adjacent a lower end portion of the water heater becoming entrained in the air intake of the water. It is theorized that such vapors might cause secondary combustion to occur within the confines of the water heater combustion chamber.
Various proposals have recently been made to prevent extraneous flammable vapors from entering a water heater combustion chamber and becoming ignited therein. Such proposals typically entail disposing a flammable vapor sensor for impingement by extraneous flammable vapors, and shutting down firing of the water heater, either by terminating fuel flow or combustion air flow to the water heater, in response to the sensor""s detection of flammable vapors.
These previous proposals are typically incorporated in conjunction with a flame arrestor plate forming a bottom exterior wall of the combustion chamber and having a series of xe2x80x9cflame quenchingxe2x80x9d openings therein which permit flammable vapors to enter the combustion chamber, but prevent combustion chamber flames from passing outwardly through such openings.
Flammable vapor sensors, like most electrical components, are subject to failure and, if their sensitivities are not carefully adjusted, may cause xe2x80x9cnuisancexe2x80x9d tripping of the safety system in a manner unnecessarily terminating or preventing firing of the water heater. Additionally, perforated flame arrestor plates may be prone to clogging with lint in certain operating environments, thereby undesirably reducing the combustion efficiency of the water heater.
As can be seen from the foregoing, it would be desirable to provide a fuel-fired heating appliance, such as a gas-fired water heater, with a flammable vapor control system for substantially preventing entry into and combustion within the combustion chamber of extraneous flammable vapors externally adjacent a bottom portion of the appliance, without the use of a flammable vapor sensor or a flame arrestor, and without terminating the firing of the appliance when it is exposed to external extraneous flammable vapors.
In carrying out principles of the present invention, in accordance with a preferred embodiment thereof, a fuel-fired heating apparatus, representatively a gas-fired water heater, is provided which has top and bottom portions and comprises a combustion chamber at its bottom portion, a burner structure operative to create hot combustion products within the combustion chamber, and a vent structure having an inlet portion communicated with the combustion chamber, and a discharge portion disposed adjacent the top portion of the water heater. The vent structure is operative, during firing of the water heater, to create a draft that draws the created hot combustion products through the vent structure toward the discharge portion thereof. While the invention is representatively embodied in a fuel-fired water heater, it may alternatively be embodied in another type of fuel-fired heating appliance such as, for example, a boiler, air heating furnace or the like.
In one illustrative version thereof, the vent structure is a forced draft vent structure including a flue extending upwardly from the combustion chamber, through water stored in a tank portion of the water heater, and a draft inducer fan connected to an upper end portion of the flue and forming part of the discharge portion of the vent structure, In another illustrative version thereof, the vent structure is a natural draft vent structure in which the draft inducer fan is eliminated and replaced with an upward extension of the flue.
According to a key aspect of the present invention, the water heater (or other type of fuel-fired heating apparatus as the case may be) in either of its forced draft and natural draft versions is provided with a specially designed flammable vapor control system which, during operational firing of the water heater, functions to substantially prevent entry into and combustion within the water heater""s combustion chamber of extraneous flammable vapors externally adjacent the bottom portion of the water heater, emanating for example from a flammable liquid spill on a floor area near the water heater, without detecting the extraneous flammable vapors or terminating the firing of the water heater.
In a representative embodiment thereof the flammable vapor control system includes a dilution air flow passage coupled to the discharge portion of the vent structure, isolated from direct communication with the combustion chamber, and having an inlet portion positioned externally adjacent the bottom portion of the water heater. The dilution air flow passage is representatively defined by an external conduit structure and functions, during firing of the water heater, to draw both dilution air and the extraneous flammable vapors upwardly from exteriorly adjacent the bottom portion of the water heater into the discharge portion of the vent structure for discharge therefrom.
The flammable vapor control system also includes a combustion air flow passage representatively defined by a combustion air inlet duct having an inlet disposed in an elevated relationship with the bottom portion of the water heater, preferably at its top portion, and an outlet which is preferably directly communicated with the interior of the combustion chamber. During operational firing of the water heater, the combination of (1) the dilution air inlet being positioned adjacent the floor near the bottom portion of the water heater, and thus in effect xe2x80x9cvacuuming upxe2x80x9d nearby flammable vapors, and (2) the combustion air duct inlet being adjacent the top portion of the water heater, serves to preclude entry of the flammable vapors into and combustion within the combustion chamber without either detecting the flammable vapors, for example by employing a flammable vapor sensor, or terminating firing of the water heater or other type of fuel-fired heating apparatus, for example by terminating combustion air flow and/or fuel flow thereto.
Preferably, all of the combustion air delivered to the combustion chamber interiorly traverses the combustion air inlet duct which is directly coupled to the combustion chamber for delivery of ambient combustion air thereinto. Accordingly, in a preferred embodiment of the water heater the bounding wall structure of its combustion chamber is devoid of flame quenching inlet openings which might tend to become clogged during the operational life of the water heater.